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Date: Tue, 13 Mar 2007 11:41:09 -0700 (PDT)
From: "Suresh Thalamati (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-2020) Change file option for syncing log
 file to disk from rws to rwd
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    [ https://issues.apache.org/jira/browse/DERBY-2020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12480516 ] 

Suresh Thalamati commented on DERBY-2020:
-----------------------------------------

Olav, 

Thanks for finding  more details about rws/rwd. 

1) I would avoid using a temp file to check if rws/rwd is correctly  
working or not. On some OS , temp files use a differ file system. 
Derby can be configured to use a different temp directory than the default
location, which can potentially be on a different file system.

I belive the check should be on log directory , where the log actually 
will be stored.

 
2) If you use "rwd" to open a file and crash while appending. 
On recovery  does it give correct length of the file ? 

> Change file option for syncing log file to disk from rws to rwd
> ---------------------------------------------------------------
>
>                 Key: DERBY-2020
>                 URL: https://issues.apache.org/jira/browse/DERBY-2020
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions: 10.3.0.0
>            Reporter: Olav Sandstaa
>         Assigned To: Olav Sandstaa
>         Attachments: disk-cache.png, no-disk-cache.png, rwd.diff, rwd.stat
>
>
> For writing the transaction log to disk Derby uses a
> RandomAccessFile. If it is supported by the JVM, the log files are
> opened in "rws" mode making the file system take care of syncing
> writes to disk. "rws" mode will ensure that both the data and the file
> meta-data is updated for every write to the file. On some operating
> systems (e.g. Solaris) this leads to two write operation to the disk
> for every write issued by Derby. This is limiting the throughput of
> update intensive applications.  If we could change the file mode to
> "rwd" this could reduce the number of updates to the disk.
> I have run some simple tests where I have changed mode from "rws" to
> "rwd" for the Derby log file. When running a small numbers of
> concurrent client threads the throughput is almost doubled and the
> response time is almost halved. I will attach some graphs that show
> this when running a given number of concurrent "tpc-b" like clients. These
> graphs show the throughput when running with "rws" and "rwd" mode when the
> disk's write cache has been enabled and disabled.
> I am creating this Jira to have a place where we can collect
> information about issues both for and against changing the default
> mode for writing to log files.

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